Scottish independence will lead to higher food bills and will prove costly for producers trading over the border, warned the former boss of Sainsbury's Justin King.

King said the cost of doing business in Scotland is already higher than the rest of the UK and therefore an independent country would carry an extra financial burden due to the borders.

"It is more expensive to do business in Scotland today. Business rates are higher, distribution costs are higher," said King, who left Sainsbury's after a decade as chief executive.

"If Scotland was to be an independent country, with businesses run separately in Scotland - as inevitably will be the case - prices would be higher.

"When you invest in a shop you've got to take a 25-year view. That's been almost impossible for the last couple of years - and probably for the next couple of years too, until we are clear what the tax and spend regime is going to look like.

"I don't think we are going to see a supermarket - and retailers more generally - rushing to invest until they can have really good long-term line of sight."

Scottish people will vote in an independence referendum on 18 September, 2014, and will be asked the straight "yes/no" question: "Should Scotland be an independent country?"

The latest YouGov poll is the second survey this week to show that the No vote has regained the lead position by a few points.

Elsewhere, other retailers John Lewis Partnership and Asda also warned of food bill hikes if Scots vote for independence.

"It does cost more money to trade in parts of Scotland, and therefore those higher costs in the event of a Yes vote are more likely to passed on," said John Lewis chairman Sir Charlie Mayfield.

"There are economic consequences to a Yes vote".

Asda's president Andy Clarke, president and chief executive of Asda said: "If we were no longer to operate in one state with one market and - broadly - one set of rules, our business model would inevitably become more complex. We would have to reflect our cost to operate here."